The pixel sizes of image sensors were 3 μm around 2000 and 2 μm or less in 2007. Furthermore, image sensors having a pixel size of 1.1 μm were put into practical use in 2012. With further miniaturization of pixels at this pace, image sensors having a pixel size of 1 μm or less are expected to be put into practical use within the next few years.
However, even with the latest fine processing technology, a space available for a photodiode is limited (far smaller than 50% of the area of a pixel). This is because most of the area of the pixel is occupied by electronic components (such as a field-effect transistor) necessary for driving a drive circuit.
To solve this problem, a patent literature introduced below discloses a solid-state imaging device including, as an upper layer, a photoelectric conversion film for capturing light and converting the light into an electrical signal.
FIG. 9 is a cross-sectional view of the conventional solid-state imaging device disclosed in the patent literature. The solid-state imaging device illustrated in FIG. 9 includes wells formed in a silicon substrate for accumulating charges, an insulating film above the wells, pixel electrodes 805 on the surface of the insulating film, an organic photoelectric conversion film 802 which is above the insulating film and connected to the pixel electrodes 805, and a counter electrode 804, a protective film 806, an electrode connected to the counter electrode 803, and a peripheral pad 801.